[0004] 該爆震極限亦可藉由將外部EGR氣體導入汽缸內來改善。此外，當該外部EGR氣體被導入時，該爆震極限可藉由使用低速凸輪而在無需仰賴提早關閉該進氣閥下獲得改善。亦即，當該外部EGR氣體被使用時，被注入到汽缸內的空氣量即使是在該進氣閥的關閉因在高負荷區的低速側使用高速凸輪而被提早的時候亦可被增加。此外，當增壓器被驅動時，該增壓操作可進一步提高被注入到汽缸內的空氣量。因此，該增壓引擎在高負荷區的低速側的輸出可被進一步提高。 [0005] 然而，EGR率(其被表示為外部EGR氣體與進氣空氣的比率)通常被設計成使得一最適目標值是依據引擎的操作狀態來選擇，這和上文所述的兩種進氣凸輪的情形相同。該目標EGR率通常被設定至一與該高負荷區相鄰的中等負荷區內的最高數值。因此，當該引擎的操作狀態從該中等負荷區換至高負荷區時會發生問題。詳言之，該問題是起因於當該引擎的操作狀態從該中等負荷區換至高負荷區時該目標EGR率下降使得爆震極限因而被降低。因此，一種有別於傳統的改良之結合多種進氣凸輪的切換和EGR率的改良必須被提出，用以提高該增壓引擎的輸出。 [0006] 本發明抑制當操作狀態從EGR率目標值很高的操作區域轉換至EGR率目標值很低的操作區域時渦輪增壓引擎中引擎輸出的減低，該渦輪增壓引擎被建構來根據一依據該操作狀態所選取的進氣凸輪和該EGR率的組合來提高引擎輸出。 [0007] 本發明的第一態樣係關於一種引擎系統。該內燃機系統包括一渦輪增壓引擎和一電子控制單元。該渦輪增壓引擎包括多個凸輪輪廓不同的進氣凸輪、一EGR系統、及一點火裝置。該等進氣凸輪被建構來驅動一進氣閥。該EGR系統被建構來將流經一廢氣系統的廢氣(如，外部EGR氣體)導入一進氣系統。該點火裝置被建構來將汽缸內的空氣-燃料混合物點火。該電子控制單元被建構來依據一以引擎扭矩和引擎轉速來識別的操作狀態設定一EGR率的目標值。該EGR率被表示為外部EGR氣體與進氣空氣的比率。在該EGR率的目標值被設定至一指定的EGR率的一第一操作區域內，該電子控制單元被建構來選取一第一凸輪作為該進氣閥的驅動凸輪且被建構來將該進氣閥的關閉時機設定至第一曲柄角度區段。該第一曲柄角度區段包括一曲柄角度，其在該引擎轉速和渦輪增壓壓力被固定的情況下提供最高的吸入效率(suction efficiency)。在該第二操作區域中，該電子控制單元被建構來選取一第二凸輪作為該驅動凸輪，該第二凸輪在閥開啟持續時間和抬升量方面小於該第一凸輪、且被建構來將該關閉時機設定至一第二曲柄角度區段並將該點火裝置的該點火時機改變至一比該點火裝置在該第一操作區域中的點火時機更提前的一側。該第二操作區域被設置為比該第一操作區域更靠近高速側。該第二操作區域讓該EGR率的目標值被設定至比該指定的EGR率更低的數值。該第二曲柄角度區段被置於比該第一曲柄角度區段更提前的一側，且在吸入效率低方面於該第一曲柄角度區段。 [0008] 藉此構造，當該操作狀態是處在該第一操作區域中時，該第一凸輪可被選取作為該進氣閥的驅動凸輪，且該進氣閥可在該第一曲柄角度區段內被關閉。當該操作狀態是處在該第一操作區域中時，該EGR率的高目標值被設定在高值，因此該爆震極限為高。該第一曲柄角度區段包括一曲柄角度，其在該引擎轉速和渦輪增壓壓力被固定的情況下提供最高的吸入效率。因此，引擎輸出可藉由選用該第一凸輪和在該第一曲柄角度區段關閉該進氣閥而被提高。 [0009] 藉此構造，當該操作狀態是處在該第二操作區域中時，該第二凸輪可被選取作為該進氣閥的驅動凸輪、該進氣閥可在該第二曲柄角度區段內被關閉、且該空氣-燃料混合物被點燃的點火時機可以比在第一操作區域內的點火時機提前。當操作狀態處在第二操作區域內時，該EGR率的目標值被設定至比第一操作區域內的操作狀態時的該EGR率被設定的目標值低。因此，該爆震極限下降。就此而言，該第二凸輪在閥開啟持續時間和抬升量方面小於第一凸輪，且該第二曲柄角度區段被設置在比第一曲柄角度區段更為提前側且在吸入效率方面低於該第一曲柄角度區段。因此，當該第二凸輪被選用且進氣閥在第二曲柄角度區段被關閉時，該吸入效率被降低，且爆震極限的下降可被抑制。此外，當空氣-燃料混合物是在比第一操作區域的點火時機更提前的點火時機被點燃時，該吸入效率的下降可被補償，且爆震極限的下降可被抑制。 [0010] 在該內燃機系統中，該電子控制單元可被建構成等待驅動凸輪的切換，直到實際EGR率的改變在驅動凸輪隨著操作狀態從第一操作區域變換至第二操作區域而從第一凸輪切換至第二凸輪時被完成為止。 [0011] 當EGR率的目標值被改變時，改變被反應在一帶著時間遲滯的實際EGR率上。當該驅動凸輪在該實際EGR率改變的同時被切換時，燃燒變得不穩定且扭矩波動增加。藉此構造，從第一凸輪切換至第二凸輪可等待驅動凸輪的切換，直到實際EGR率的改變被完成為止。因此，穩定的燃燒和較少的扭矩波動可被達成。 [0012] 在該內燃機系統中，該渦輪增壓引擎可包括一將燃料供應至汽缸內的噴油器。該電子控制單元可被建構來控制該噴油器，使得當操作狀態是在第一驅動範圍時，燃料在壓縮行程中被噴入。該電子控制單元可被建構來控制該噴油器，使得當操作狀態是在第二驅動範圍時，燃料在進氣行程中被噴入。 [0013] 該第二凸輪在閥開啟持續時間和抬升量方面比第一凸輪小。因此，當該第二凸輪被選取作為驅動凸輪時，在汽缸內的紊流會變得比該第一凸輪被選取作為驅動凸輪時所產生的紊流小，這導致燃燒速度下降。藉此構造，該噴油器可被控制，使得當該操作狀態是在該第二操作狀態時，燃料是在進氣行程被噴入。這可促進進氣空氣和燃料的混合，使得引擎輸出的降低可被抑制。 [0014] 在該內燃機系統中，該電子控制單元可被建構成等待驅動凸輪的切換，直到該噴油器的噴油時機的改變在驅動凸輪隨著操作狀態從第一操作區域變換至第二操作區域而從第一凸輪切換至第二凸輪時被完成為止。 [0015] 當該驅動凸輪在該噴油器的噴油時機改變的同時被切換時，燃燒變得不穩定且扭矩波動增加。藉此構造，從第一凸輪切換至第二凸輪可等待，直到該噴油器的噴油時機的改變被完成為止。因此，穩定的燃燒和較少的扭矩波動可被達成。 [0016] 在該內燃機系統中，該渦輪增壓引擎可包括一支撐多個進氣凸輪的凸輪軸、及一轉動相位改變機構，其改變該凸輪軸相對於曲柄軸的轉動相位。當驅動凸輪隨著操作狀態從第一操作區域轉換至第二操作區域而從第一凸輪切換至第二凸輪時，該電子控制單元可被建構來改變該轉動相位，使得該吸入效率在驅動凸輪切換之前和之後一致，並等待該驅動凸輪的切換直到該轉動相位的改變被完成為止。 [0017] 藉此構造，該凸輪軸相對於曲柄軸的轉動相位可被改變，使得該吸入效率在驅動凸輪切換之前和之後一致。該驅動凸輪的切換可被等待直到該轉動相位的改變被完成為止。因此，燃燒在驅動凸輪的切換之前和之後可被穩定，且扭矩波動可被抑制。 [0018] 在該內燃機系統中，該渦輪增壓引擎可包括一液冷式中間冷卻器，其冷卻流經該進氣系統的進氣空氣、及一熱交換器，其與該中間冷卻器共用冷卻劑。該電子控制單元可被建構成在下面的條件i)及ii)皆被滿足時不實施驅動凸輪的切換:i)該驅動凸輪隨著操作狀態從第一操作區域轉換至第二操作區域而從第一凸輪切換至第二凸輪，及ii)送入該中間冷卻器和該熱交換器內的冷卻劑的溫度高於一指定溫度。 [0019] 藉此構造，當送入該中間冷卻器和該熱交換器內的冷卻劑的溫度高於該指定溫度時，該驅動凸輪本身的切換可被禁止。因此，可抑制該熱交換器內的過高的溫度上升。 [0020] 在該內燃機系統中，在一第三操作區域內，該電子控制單元可被建構來選取一第三凸輪作為該驅動凸輪，該第三凸輪在該抬升量方面小於該第一凸輪且在閥開啟持續時間方面小於該第二凸輪，且可被建構來將該關閉時機設定至一第三曲柄角度區段並將該點火裝置的點火時機改變至一比在第一操作區域內的點火裝置的點火時機更提前的一側。該第三操作區域可被設置在比該第一操作區域更靠近低速側。該第三操作區域可讓該EGR率的目標值被設定至一比該指定的EGR率低的數值。該第三曲柄角度區段可被設置在比第一曲柄角度區段更提前的一側，且比該第二曲柄角度區段窄。 [0021] 藉此構造，當操作狀態處於該第三操作區域內時，該第三凸輪可被選作為該進氣閥的驅動凸輪，該進氣閥可在該第三曲柄角度區段內被關閉，且該空氣-燃料混合物可在比該第一操作區域內的點火時機更提前的點火時機被點火。當該操作狀態處於該第三操作區域內時，該EGR率的目標值被設定為低於當該操作狀態處於該第一操作區域時的目標值。因此，該爆震極限下降。就此而言，該第三凸輪在該抬升量方面小於該第一凸輪且在閥開啟持續時間方面小於該第二凸輪。該第三曲柄角度區段亦被置於一比該第一曲柄角度區段更提前的一側且比該第二曲柄角度區段窄。因此，當該第三凸輪被選用作且該進氣閥在該第三曲柄角度區段內被閉時，吸入效率可被降低，且該爆震極限可被抑制。此外，當空氣-燃料混合物是在比第一操作區域的點火時機更提前的點火時機被點燃時，該吸入效率的下降可被補償，且爆震極限的下降可被抑制。 [0022] 在該內燃機系統中，該渦輪增壓引擎可具有11或更高的幾何壓縮比。 [0023] 藉此構造，具有11或更高的幾何壓縮比的該渦輪增壓引擎的引擎輸出可被提高。 [0024] 本發明的第二態樣係關於一種內燃機的控制方法。該內燃機包括一渦輪增壓引擎和一電子控制單元。該渦輪增壓引擎包括多個凸輪輪廓不同的進氣凸輪、一EGR系統、和一點火裝置。該等進氣凸輪被建構來驅動一進氣閥。該EGR系統被建構將流經一廢氣系統的廢氣(如，外部EGR氣體)導入一進氣系統。該點火裝置被建構來將汽缸內的空氣-燃料混合物點火。該電子控制單元被建構來依據一以引擎扭矩和引擎轉速識別的操作狀態來設定一EGR率的目標值。該EGR率被表示為該外部EGR氣體與進氣空氣的比率。該控制方法包括在該EGR率的目標值被設定至一指定的EGR率的一第一操作區域內，該電子控制單元選取一第一凸輪作為該進氣閥的驅動凸輪且該電子控制單元將該進氣閥的關閉時機設定至第一曲柄角度區段，該第一曲柄角度區段包括一曲柄角度，其在該引擎轉速和渦輪增壓壓力被固定的情況下提供最高的吸入效率、且在一第二操作區域中，該電子控制單元選取一第二凸輪作為該驅動凸輪，該電子控制單元將該關閉時機設定至一第二曲柄角度區段(其位在比該第一曲柄角度區段更提前的一側)，且該電子控制單元將該點火裝置的該點火時機改變至比該點火裝置在該第一操作區域中的點火時機更提前的一側。該第二操作區域被設置為比該第一操作區域更靠近高速側。該第二操作區域讓該EGR率的目標值被設定至比該指定的EGR率更低的數值。該第二凸輪在閥開啟持續時間和抬升量方面小於該第一凸輪。該第二曲柄角度區段在吸入效率方面低於該第一曲柄角度區段。 [0025] 藉此構造，當該操作狀態是處在該第一操作區域中時，該第一凸輪可被選取作為該進氣閥的驅動凸輪，且該進氣閥可在該第一曲柄角度區段內被關閉。當該操作狀態是處在該第一操作區域中時，該EGR率的目標值被設定在高值，因此該爆震極限為高。該第一曲柄角度區段包括一曲柄角度，其在該引擎轉速和渦輪增壓壓力被固定的情況下提供最高的吸入效率。因此，引擎輸出可藉由選用該第一凸輪和在該第一曲柄角度區段關閉該進氣閥而被提高。[0004] The knock limit can also be improved by introducing external EGR gas into the cylinder. In addition, when the external EGR gas is introduced, the knock limit can be improved by using a low-speed cam without relying on closing the intake valve early. That is, when the external EGR gas is used, the amount of air injected into the cylinder can be increased even when the closing of the intake valve is early due to the use of a high-speed cam on the low-speed side of the high-load region. In addition, when the supercharger is driven, the supercharging operation can further increase the amount of air injected into the cylinder. Therefore, the output of the supercharged engine on the low speed side of the high load region can be further improved. [0005] However, the EGR rate (which is expressed as the ratio of external EGR gas to intake air) is usually designed such that an optimum target value is selected according to the operating state of the engine, which is different from the two The situation with the air cam is the same. The target EGR rate is usually set to the highest value in a medium load zone adjacent to the high load zone. Therefore, a problem occurs when the operating state of the engine is changed from the medium load region to the high load region. In detail, the problem is caused by the decrease in the target EGR rate when the operating state of the engine is changed from the medium load region to the high load region so that the knock limit is lowered. Therefore, an improvement that combines the switching of multiple intake cams and the EGR rate, which is different from the conventional improvement, must be proposed to increase the output of the supercharged engine. [0006] The present invention suppresses a decrease in engine output in a turbocharged engine when the operating state is switched from an operating region with a high EGR rate target value to an operating region with a low EGR rate target value, the turbocharged engine is constructed to A combination of the intake cam selected according to the operating state and the EGR rate increases engine output. [0007] The first aspect of the invention relates to an engine system. The internal combustion engine system includes a turbocharged engine and an electronic control unit. The turbocharged engine includes a plurality of intake cams with different cam profiles, an EGR system, and an ignition device. The intake cams are constructed to drive an intake valve. The EGR system is constructed to introduce exhaust gas (eg, external EGR gas) flowing through an exhaust gas system into an intake system. The ignition device is constructed to ignite the air-fuel mixture in the cylinder. The electronic control unit is constructed to set a target value of EGR rate based on an operating state identified by engine torque and engine speed. The EGR rate is expressed as the ratio of external EGR gas to intake air. In a first operating area where the target value of the EGR rate is set to a specified EGR rate, the electronic control unit is constructed to select a first cam as the drive cam of the intake valve and is constructed to control the intake The closing timing of the air valve is set to the first crank angle section. The first crank angle section includes a crank angle that provides the highest suction efficiency when the engine speed and turbocharge pressure are fixed. In the second operating area, the electronic control unit is configured to select a second cam as the drive cam, the second cam is smaller than the first cam in terms of valve opening duration and lift amount, and is configured to control The closing timing is set to a second crank angle section and the ignition timing of the ignition device is changed to a side earlier than the ignition timing of the ignition device in the first operation area. The second operation area is set closer to the high-speed side than the first operation area. The second operating region allows the target value of the EGR rate to be set to a lower value than the specified EGR rate. The second crank angle section is placed on a side earlier than the first crank angle section, and is lower in the suction efficiency than the first crank angle section. [0008] With this configuration, when the operating state is in the first operating region, the first cam may be selected as the driving cam of the intake valve, and the intake valve may be at the first crank angle The section is closed. When the operating state is in the first operating region, the high target value of the EGR rate is set at a high value, so the knock limit is high. The first crank angle section includes a crank angle that provides the highest suction efficiency when the engine speed and turbocharge pressure are fixed. Therefore, the engine output can be increased by selecting the first cam and closing the intake valve at the first crank angle section. [0009] With this configuration, when the operating state is in the second operating region, the second cam may be selected as the driving cam of the intake valve, the intake valve may be in the second crank angle region The ignition timing in the segment that is turned off and the air-fuel mixture is ignited may be earlier than the ignition timing in the first operation area. When the operating state is in the second operating region, the target value of the EGR rate is set to be lower than the target value of the EGR rate when the operating state in the first operating region is set. Therefore, the knock limit decreases. In this regard, the second cam is smaller than the first cam in terms of the duration of valve opening and the amount of lift, and the second crank angle section is provided on the more advanced side than the first crank angle section and low in suction efficiency At the first crank angle section. Therefore, when the second cam is selected and the intake valve is closed at the second crank angle section, the suction efficiency is reduced, and the drop in knock limit can be suppressed. In addition, when the air-fuel mixture is ignited at an ignition timing earlier than that of the first operation area, the decrease in the suction efficiency can be compensated, and the decrease in knock limit can be suppressed. [0010] In the internal combustion engine system, the electronic control unit may be configured to wait for the switching of the driving cam until the actual EGR rate changes after the driving cam changes from the first operating region to the second operating region It is completed when one cam is switched to the second cam. [0011] When the target value of the EGR rate is changed, the change is reflected in the actual EGR rate with time lag. When the drive cam is switched while the actual EGR rate changes, combustion becomes unstable and torque fluctuations increase. With this configuration, switching from the first cam to the second cam can wait for the switching of the driving cam until the change of the actual EGR rate is completed. Therefore, stable combustion and less torque fluctuations can be achieved. [0012] In the internal combustion engine system, the turbocharged engine may include an injector that supplies fuel into the cylinder. The electronic control unit may be configured to control the fuel injector so that when the operating state is in the first driving range, fuel is injected during the compression stroke. The electronic control unit may be configured to control the injector so that when the operating state is in the second driving range, fuel is injected in the intake stroke. [0013] This second cam is smaller than the first cam in terms of the valve opening duration and the lift amount. Therefore, when the second cam is selected as the driving cam, the turbulence in the cylinder becomes smaller than the turbulence generated when the first cam is selected as the driving cam, which results in a decrease in the combustion speed. With this configuration, the injector can be controlled so that when the operating state is in the second operating state, fuel is injected in the intake stroke. This can promote the mixing of intake air and fuel, so that the reduction in engine output can be suppressed. [0014] In the internal combustion engine system, the electronic control unit may be configured to wait for the switching of the driving cam until the change of the injection timing of the fuel injector changes in the driving cam from the first operating region to the second with the operating state The operation area is completed when switching from the first cam to the second cam. [0015] When the drive cam is switched while the injection timing of the injector is changed, combustion becomes unstable and torque fluctuation increases. With this configuration, switching from the first cam to the second cam can wait until the change of the injection timing of the injector is completed. Therefore, stable combustion and less torque fluctuations can be achieved. [0016] In the internal combustion engine system, the turbocharged engine may include a camshaft supporting a plurality of intake cams, and a rotational phase changing mechanism that changes the rotational phase of the camshaft relative to the crankshaft. When the driving cam is switched from the first cam to the second cam as the operating state is switched from the first operating area to the second operating area, the electronic control unit can be constructed to change the rotational phase so that the suction efficiency is Before and after switching, they are the same and wait for the switching of the driving cam until the change of the rotation phase is completed. [0017] With this configuration, the rotational phase of the cam shaft relative to the crank shaft can be changed so that the suction efficiency is consistent before and after the driving cam is switched. The switching of the driving cam may be waited until the change of the rotation phase is completed. Therefore, combustion can be stabilized before and after the switching of the driving cam, and torque fluctuation can be suppressed. [0018] In the internal combustion engine system, the turbocharged engine may include a liquid-cooled intercooler that cools the intake air flowing through the intake system and a heat exchanger that is shared with the intercooler Coolant. The electronic control unit can be constructed so that the following conditions i) and ii) are not satisfied when the driving cam is switched: i) The driving cam switches from the first operating area to the second operating area as the operating state changes The first cam is switched to the second cam, and ii) the temperature of the coolant fed into the intercooler and the heat exchanger is higher than a specified temperature. [0019] With this configuration, when the temperature of the coolant fed into the intercooler and the heat exchanger is higher than the specified temperature, the switching of the drive cam itself can be prohibited. Therefore, an excessively high temperature rise in the heat exchanger can be suppressed. [0020] In the internal combustion engine system, in a third operating area, the electronic control unit may be constructed to select a third cam as the driving cam, the third cam is smaller in the lift amount than the first cam and It is shorter than the second cam in terms of the valve opening duration, and can be constructed to set the closing timing to a third crank angle section and change the ignition timing of the ignition device to an ignition ratio in the first operating area The side where the ignition timing of the device is more advanced. The third operation area may be set closer to the low-speed side than the first operation area. The third operating area allows the target value of the EGR rate to be set to a value lower than the specified EGR rate. The third crank angle section may be disposed on a side earlier than the first crank angle section, and narrower than the second crank angle section. [0021] With this configuration, when the operating state is within the third operating region, the third cam may be selected as the driving cam of the intake valve, and the intake valve may be selected within the third crank angle section It is off, and the air-fuel mixture can be ignited at an ignition timing that is earlier than the ignition timing in the first operating area. When the operating state is within the third operating region, the target value of the EGR rate is set to be lower than the target value when the operating state is within the first operating region. Therefore, the knock limit decreases. In this regard, the third cam is smaller than the first cam in terms of the lift amount and smaller than the second cam in terms of the valve opening duration. The third crank angle section is also placed on a side earlier than the first crank angle section and narrower than the second crank angle section. Therefore, when the third cam is selected as the intake valve and the intake valve is closed in the third crank angle section, the suction efficiency can be reduced, and the knock limit can be suppressed. In addition, when the air-fuel mixture is ignited at an ignition timing earlier than that of the first operation area, the decrease in the suction efficiency can be compensated, and the decrease in knock limit can be suppressed. [0022] In the internal combustion engine system, the turbocharged engine may have a geometric compression ratio of 11 or higher. [0023] With this configuration, the engine output of the turbocharged engine having a geometric compression ratio of 11 or higher can be improved. [0024] The second aspect of the present invention relates to a control method of an internal combustion engine. The internal combustion engine includes a turbocharged engine and an electronic control unit. The turbocharged engine includes a plurality of intake cams with different cam profiles, an EGR system, and an ignition device. The intake cams are constructed to drive an intake valve. The EGR system is constructed to introduce exhaust gas (eg, external EGR gas) flowing through an exhaust gas system into an intake system. The ignition device is constructed to ignite the air-fuel mixture in the cylinder. The electronic control unit is constructed to set a target value of EGR rate based on an operating state identified by engine torque and engine speed. The EGR rate is expressed as the ratio of the external EGR gas to intake air. The control method includes that within a first operating area where the target value of the EGR rate is set to a specified EGR rate, the electronic control unit selects a first cam as the drive cam of the intake valve and the electronic control unit will The closing timing of the intake valve is set to a first crank angle section which includes a crank angle which provides the highest suction efficiency when the engine speed and turbocharge pressure are fixed, and In a second operation area, the electronic control unit selects a second cam as the driving cam, and the electronic control unit sets the closing timing to a second crank angle section (which is located in a region that is greater than the first crank angle area The more advanced side), and the electronic control unit changes the ignition timing of the ignition device to a side that is earlier than the ignition timing of the ignition device in the first operation area. The second operation area is set closer to the high-speed side than the first operation area. The second operating region allows the target value of the EGR rate to be set to a lower value than the specified EGR rate. The second cam is smaller than the first cam in terms of valve opening duration and lift amount. The second crank angle section is lower in suction efficiency than the first crank angle section. [0025] With this configuration, when the operating state is in the first operating region, the first cam may be selected as the driving cam of the intake valve, and the intake valve may be at the first crank angle The section is closed. When the operating state is in the first operating region, the target value of the EGR rate is set at a high value, so the knock limit is high. The first crank angle section includes a crank angle that provides the highest suction efficiency when the engine speed and turbocharge pressure are fixed. Therefore, the engine output can be increased by selecting the first cam and closing the intake valve at the first crank angle section.
[0027] 本發明的實施例將根據圖式於下文中描述。應指出的是，在每一圖式中相同的元件被標示相同的參考符號以省略冗餘的描述。下面的實施例並不是要侷限本發明。 [0028] 首先，本發明的第一實施例將參考圖1至10加以描述。 [0029] 圖1是一例示依據本發明的第一實施例的系統的構造的例子的示意圖。示於圖1中的系統是一用於安裝在車輛上的內燃機的系統。示於圖1中的該系統包括一作為驅動源的內燃機10。該內燃機10是四行程汽缸引擎，且亦是一直列三汽缸引擎。該內燃機10汽缸數和汽缸配置並沒有特別限制。該內燃機10具有一11或更高之相對高的幾何壓縮比。該內燃機10的每一汽缸和一進氣管12及一排氣管14相聯通。 [0030] 首先提供該內燃機10的進氣系統的描述。在該進氣管12的入口附近附裝了一空氣清淨器16。一渦輪增壓器18的壓縮機18a被設置在該空氣清淨器16的下游。被一設置在該排氣管14內的渦輪18b的轉動所驅動的該壓縮機18a壓縮進氣空氣。一電子控制式節流閥20被設置在該壓縮機18a的下游。一連接至每一汽缸的進氣埠的進氣歧管22被設置在該節流閥20的下游。該進氣歧管22包含一液冷式中間冷卻器24。流入該中間冷卻器24的進氣空氣透過與一流經冷卻管26的冷卻劑的熱交換而被冷卻。 [0031] 現將提供該內燃機10的廢氣系統的描述。該排氣管14配備有該渦輪增壓器18的渦輪18b。該渦輪18b與該壓縮機18a相耦合。該渦輪18b是用流經該排氣管14的廢氣的能量來轉動。一繞過該渦輪18b的旁通管28被設置在該排氣管14的中間處。該旁通管28被設置有一廢氣閘閥(WGV)30。該WGV30在該渦輪18b的上游側的排氣管壓力(背壓)高於一規定的數值時即被打開。當該WGV30被打開時，一些流經該渦輪18b的上游部分的廢氣就會流經該旁通管28進入到該渦輪18b的下游部分。用來潔淨該廢氣的觸媒32，34被設置在該渦輪18b的下游。 [0032] 接下來，該內燃機10的一EGR系統將被描述。該內燃機10包括一低壓迴圈-EGR(LPL-EGR)系統36。該LPL-EGR系統36包括一EGR管38，其將該排氣管14位在觸媒32和觸媒34之間的部分連接至該進氣管12位在該壓縮機18a的上游側的部分。一液冷式EGR冷卻器40被設置在該EGR管38的中間處。流入該EGR冷卻器40的廢氣(即，外部EGR氣體)透過和一流經該冷凝管42的冷卻劑的熱交換而被冷卻。一電子控制式EGR閥44被設置在該EGR冷卻器40的下游。當該EGR閥44的打開程度被改變時，從該EGR管38流入該進氣管12之該外部EGR氣體的流率即被改變。隨著該EGR閥44的打開程度變大，該EGR率即變高。 [0033] 現將提供該內燃機10的閥系統的描述。圖2是一例示兩種包括在依據本發明的第一實施例的系統內的進氣凸輪的凸輪輪廓(代表抬升量和閥開啟持續時間的至少一者的凸輪輪廓，且這適用於下面的描述)的例子的解釋性圖式。應指出的是，“閥開啟持續時間”係指閥被保持打開的時間長度，以度為單位。如圖2中所示，依據第一實施例的系統包括兩種進氣凸輪：正常的凸輪；和小凸輪。該小凸輪在閥開啟持續時間和抬升量方面比該正常凸輪小。該正常凸輪和該小凸輪被一凸輪軸支撐，該凸輪軸和一曲柄軸同步轉動。兩個正常凸輪和小凸輪配對被支撐在每一汽缸內。這是因為每一汽缸被設置有兩個進氣閥。然而，在本發明中，每一汽缸的進氣閥數量可以是一個、或可以是三個或更多個。 [0034] 支撐該正常凸輪和該小凸輪的該凸輪軸被設置一可變的閥定時機構(VVT)。該VVT是一種藉由改變該凸輪閥相對於該曲柄軸的轉動相位差來改變進氣閥的閥開啟特性的機構。該VVT包括一外殼，其透過一定時鏈及類此者與該曲柄軸相耦合、一葉片本體，其被設置在該外殼內且被附裝至該凸輪軸的端部。當液壓被供應至一被該外殼和該葉片本體分隔的液壓室的內部時，該葉片本體可相對於該外殼被轉動。因此，該凸輪軸相對於該曲柄軸的轉動相位差即可被改變。被供應至該VVT的液壓是由一設置在一液壓供應管線內的液壓控制閥來控制。該VVT的構造是眾所周知的。因為對於本發明中的VVT的構造沒有特別的限制，所以關於VVT的進一步描述將被省略。 [0035] 再次參考圖1，該系統的構造例子將被進一步描述。示於圖1中的系統包括一作為控制器的電子控制單元(ECU)50。該ECU50包括隨機存取記憶體(RAM)、唯讀記憶體(ROM)、及微處理器(CPU)。該ECU50從安裝在車輛上的各種感測器取得訊號並處理這些訊號。該等感測器包括空氣流量計52、曲柄角度感測器54、渦輪增壓壓力感測器56、冷卻劑溫度感測器58、背壓感測器60、及氣體溫度感測器62。該空氣流量計52被設置在該空氣清淨器16附近以偵測吸入空氣的量。該曲柄角度感測器54輸出一對應於該曲柄軸的轉動角度的訊號。該渦輪增壓壓力感測器56偵測該進氣管在該節流閥20的上游側的部分的壓力(渦輪增壓壓力)。該冷卻劑溫度感測器58偵測在該內燃機10內的冷卻劑的溫度。該背壓感測器60偵測該排氣管在該渦輪18b的上游側的部分的壓力(背壓)。該氣體溫度感測器62偵測在該EGR冷卻器40的出口部分的廢氣的溫度。 [0036] 該ECU50處理從該等各種感測器取得的訊號，並依據指定的控制程式操作各種作動器。該等各種作動器包括節流閥20及該WGV30。該等作動器亦包括一將燃料噴入汽缸的噴油器70、將汽缸內的空氣-燃料混合物點火的點火裝置72、VVT74、及凸輪切換機構76，其切換驅動該進氣閥的進氣凸輪(下文中被稱為“驅動凸輪”)。 [0037] 圖3例示目標EGR率(EGR率的目標值)和引擎操作區域之間的關係的例子。圖3的關係是根據先前的模擬來準備的。如圖3中的輪廓線所顯示的，該目標EGR率被設定至中間扭矩和中間速度區域內的最高數值。這是為了要提高在使用頻率而言特別高的該中間扭矩和中間速度區域內的EGR率以提高熱效率。較低的目標EGR率被設定給離該中間扭矩和中間速度區域較遠的周邊區域，該等周邊區域就使用頻率而言是較低的。詳言之，在高扭矩和低扭矩區域中，該目標EGR率被設定至一比該中間扭矩區域的目標EGR率低的數值。類似地，在高速區域或低速區域中，該目標EGR率被設定至一比該中等速度區域的目標EGR率低的數值。在第一實施例中，圖3所示的關係被儲存在該ECU的ROM內。該EGR閥的打開程度是藉由將實際操作狀態應用到該關係上來加以控制的。 [0038] 在第一實施例中，為了要提高引擎輸出，結合該目標EGR率和該進氣閥的關閉時間的引擎控制被實施。圖4例示引擎操作區域和驅動該進氣閥的凸輪之間的關係的例子。如圖4所示，在多數的操作區域內，正常的凸輪被選用。該小凸輪只在高扭矩和高速度區域內被選用。在第一實施例中，圖4所示的關係被儲存在ECU的ROM中。由該凸輪切換機構所實施的該切換操作是藉由將一實際操作狀態應用至該關係上來加以控制。 [0039] 圖5是一例示該進氣閥的關閉時間的一個例子的解釋性圖式。如圖5所示，當該驅動凸輪是該正常凸輪時，進氣閥在一位於下死點(ABDC=0)之後的曲柄角度區段CA1
內被關閉。當該驅動凸輪是該小凸輪時，進氣閥在一包括該下死點的曲柄角度區段CA2
內被關閉。圖5中所示的曲柄角度區段CA1
，CA2
具有寬度，因為進氣閥的關閉時間被VVT改變。然而，當帶有一大的抬升量的正常凸輪被用作為驅動凸輪以提高在經常使用的操作區域內的引擎輸出時，該曲柄角度區段CA1
被設定成包括可提供最大吸入效率的曲柄角度。當帶有小的抬升量的該小凸輪被用作為該驅動凸輪時，該曲柄角度區段CA2
被設定成排除可提供最大吸入效率的曲柄角度。圖5中所示的該吸入效率可在例如引擎轉速和渦輪增壓壓力被固定的操作條件下被獲得。 [0040] 在圖5中，該小凸輪在高扭矩及高速區域中被選用，因為爆震傾向於當該正常凸輪於此操作區域中被選用的時候發生。爆震傾向於在該中等扭矩區域到高扭矩區域的範圍內發生。如圖3所描述的，在該中等扭矩及中等速度區域中，該目標EGR率被設定至一高的數值。這表示爆震極限被提高。如圖3所描述的，在該高扭矩及高速區域中，該目標EGR率被設定至一比在該中等扭矩及中等速度區域中的目標EGR率低的數值。因此，當引擎操作狀態如圖3中的操作線所顯示地轉換時，該目標EGR率逐漸地增加至一最大值，然後降低至目前的操作點。因此，如果該正常凸輪在操作線的該時期持續被選用的話，則雖然爆震極限隨著目標EGR率的降低而下降，但實際壓縮比很高的狀態仍持續。因此，沒有其它選擇，只能延遲點火時機，而這導致引擎輸出下降無法避免的情況。 [0041] 為了要應付此情況，在第一實施例中，該小凸輪在高扭矩及高速區域中被選用。因此，實際壓縮比很高的狀態即可被消除，且吸入效率可被降低。這可抑制爆震極限的下降並藉以避免點火時機的延遲。在該高扭矩及高速區域中，該背壓很高。因此，當正常凸輪被選用時，該背壓大幅超過該預定值，因此該WGV被打開。然而，當該正常凸輪被切換至該小凸輪時，吸入效率被刻意地降低，這導致背壓的下降。因此，該WGV打開的程度隨著該背壓變成小於該預定值而被減小。因此，可提高該渦輪增壓壓力並藉以補償選用該小凸輪所造成之吸入效率的下降。這可提高該引擎輸出。 [0042] 圖6是一例示在本發明的第一實施例中引擎控制所獲得的效果的解釋性圖式。如圖6所示，當該正常凸輪在EGR率被降低的時候被持續地選用時，最大引擎輸出在EGR率下降之後亦隨之下降(虛線箭頭)。在第一實施例中，因為該正常凸輪在EGR率被降低的時候被切換至該小凸輪，所以最大引擎輸出的下降可被抑制(實線箭頭)。該被降低的EGR率的數值可以是零、或可以是大於零。 [0043] 現在，當該驅動凸輪從小凸輪被切換至該正常凸輪且該進氣閥的關閉時間被改變時，不僅僅是吸入效率下降，燃燒速度亦下降。圖7例示進氣閥的關閉時間和汽缸內的紊流之間的關係的例子。如圖7所示，當該驅動凸輪是小凸輪時，汽缸內的紊流變得比驅動凸輪是該正常凸輪的時候小。因此，當驅動凸輪從該正常凸輪切換至小凸輪時，燃燒速度可被減慢且引擎輸出會下降。然而，在如第一實施所示的具有高幾何壓縮比的內燃機中，和該吸入效率降低相關的該渦輪增壓壓力的提高的影響大於燃燒速地降低的影響。因此，引擎輸出的降低被抑制(參見圖6)。在此而言，在具有約10的幾何壓縮比的一般渦輪增壓引擎中，燃燒速度降低地影響變得相對較大。因此，引擎輸出傾向於被降低。 [0044] 接下來，參考圖8，第一實施例中的引擎控制的特定例子將被描述。圖8是一時間圖表，其例示本發明的第一實施例中的引擎控制的一個例子。圖8的時間圖表描繪出當引擎的操作狀態沿著圖3所示的操作線從EGR率高的區域(即，中等扭矩及中等速度區域)轉換至目標EGR率低的區域(即，高扭矩及高速區域)時的各種物理數值及控制參數的轉變。因此，在圖3所示的汽缸內的渦輪增壓壓力和空氣量大體而言持續增加的同時，圖8所示的ERG率在時間t1
下降。 [0045] 如圖8所示，該EGR率在從時間t1
到時間t2
的期間下降。這是因為該EGR閥打開的程度隨著圖3所示的目標EGR率的降低而被改變至關閉側。當EGR率下降時，該爆震極限亦下降。因此，在該EGR率被改變的同時，點火時機持續被改變至延遲側。隨著點火時機被延遲，一曲柄角度θ_Pmax(該汽缸內的壓力在此曲柄角度時變成最大)移動至延遲側。 [0046] 在第一實施例中，該驅動凸輪在該EGR率被改變時並未被切換。其原因在於，當驅動凸輪從正常凸輪被切換至小凸輪與實際EGR值的改變同時的時候，燃燒變得不穩定且扭矩波動增大。此外，驅動凸輪的切換在時間t2
(EGR率的改變在此時間點完成)時尚未開始。驅動凸輪的切換到時間t3
為止都處在待命狀態。在時間t2
，不是驅動凸輪的改變，而是燃料的噴油時機被改變至一提前側。該噴油時機從壓縮行程中的一曲柄角度被改變至進氣行程中的一曲柄角度。其理由在於，當驅動凸輪是該正常凸輪時，汽缸內的紊流可被鞏固(secured)且引擎輸出可被提高，而在驅動凸輪被切換至小凸輪之後，汽缸內的紊流降低。因此，在時間t2
，當噴油時機被提前且被改變至進氣行程中的曲柄角度時，進氣空氣和燃料的混合可被提高，使得引擎輸出的降低可被抑制。 [0047] 在第一實施例中，進氣閥的閥關閉時間在時間t2
被改變至延遲側。藉由控制VVT的液壓控制閥，在驅動凸輪是該正常凸輪的同時，該閥關閉時間被改變至延遲側，使得吸入效率在驅動凸輪的切換之前和之後是一致的。圖9是一例示進氣閥的閥關閉時間和吸入效率之間的關係的一個例子的解釋性圖式。如圖9所示，該吸入效率展示在下死點附近實質對稱於該曲柄角度的中心的特性。因為該渦輪增壓壓力的影響的關係，所以在對稱中心處的曲柄角度並沒有和該下死點重合。該正常凸輪和該小凸輪間在閥開啟持續時間上的差異在設計凸輪的相位時即已知。因此，根據圖9所示的特性，進氣閥的閥關閉時間(在此關閉時間，吸入效率在驅動凸輪的切換之前和之後是一致的)可被指認出來。 [0048] 驅動凸輪的切換是在進氣閥的閥關閉時間被VVT改變被完成的時候的時間t3
開始。其原因在於，當驅動凸輪從正常凸輪被切換至小凸輪與點火時機的改變或與該進氣閥的閥關閉時間的改變同時的時候，燃燒變得不穩定且扭矩波動增大。在時間t3
，點火時機亦被改變至該提前側。該點火時機在時間t3
的提前角度被設定至一數值，其促使該將汽缸內的壓力最大化的曲柄角度θ_Pmax和在時間t1
時的曲柄角度θ_Pmax實質相等。然而，在時間t3
的點火時機被改變至比時間t1
時的點火時機更為提前。藉由將點火時機改變至該提前側，吸入效率的下降及和驅動凸輪的切換相關的燃燒速度的降低可被補償，且引擎輸出的降低被抑制。 [0049] 如上文提到的，當小凸輪在高扭矩及高速區域中被選用時，爆震極限的降低可被抑制。因此，在時間t3
被改變的點火時機在時間t3
之後一段時間持續被進一步改變至該提前側。在時間t4
之後，當切換至小凸輪被完成時，WGV的打開程度隨著刻意降低吸入效率而減小。因此，在時間t3
之前都傾向於提高的該渦輪增壓壓力在時間t4
之後進一步提高。在汽缸內的空氣量亦隨著該渦輪增壓壓力在時間t4
之後提高而增加。因此，如圖8中最上面一欄所示，持續地提高從正常凸輪被切換至小凸輪之前和之後的引擎輸出是可能的。 [0050] 圖10例示本發明的第一實施例中由ECU執行的一處理常式(processing routine)的例子。該常式是在每一預設的控制期間(例如，每當該曲柄軸轉120度時)被執行。 [0051] 在圖10所示的該常式中，首先被決定的是該EGR氣體是否可被導入(步驟S10)。該EGR氣體是否可被導入是例如根據EGR冷卻器的冷卻限制及冷凝水限制來判定。EGR冷卻器的冷卻限制的例子包括有在EGR冷卻器的出口部分的氣體溫度、在EGR冷卻器的出口部分的冷卻劑的溫度、或該壓縮機的上游部分的氣體溫度等於或低於一指定溫度。冷凝水限制的例子包括有在該中間冷卻器的出口部分的氣體溫度等於或高於露點溫度。當該EGR冷卻限制沒有被滿足時，則判定藉由導入該EGR氣體來提高該熱效率是不能被期待的。當該冷凝水限制沒有被滿足時，則判定冷凝水沒有被產生在該中間冷卻器的出口部分中。因此，當該冷卻限制或該冷凝水限制沒有被滿足時，則判定對於外部EGR氣體有一限制，且步驟S12的處理以及後續的處理被實施(稍後將詳細說明)。 [0052] 當步驟S10的判斷結果是肯定時，則判定對於外部EGR氣體有一限制，且步驟S14的處理以及後續的處理被實施。在步驟S14中，被判斷的是該引擎的操作狀態是否處在高扭矩及高速區域。該高扭矩及高速區域對應於圖4所示的操作區域。當步驟S14的判斷結果是否定時，該目標EGR率的上限被設定至一最大值(步驟S16)、該噴油時機被設定至一在壓縮行程內的曲柄角度(步驟S18)、且該正常凸輪被選取作為該驅動凸輪(步驟S20)。因此，該引擎控制是在圖3至圖4所描述的高扭矩及高速區域以外的操作區域內被實施。 [0053] 當步驟S14的判斷結果是肯定時，則判斷小凸輪是否可被使用(步驟S22)。小凸輪是否可被使用是例如根據渦輪增壓工作限制來決定。渦輪增壓工作限制的例子包括有大氣壓力等於或高於一指定數值，或者該背壓等於或低於一指定壓力。當該渦輪增壓工作限制沒有被滿足時，則判定即使是該正常凸輪被切換至該小凸輪，該引擎輸出的提高仍無法被期待。因此，當該渦輪增壓工作限制沒有被滿足時，步驟S24的處理以及後續的處理被實施。亦即，該目標EGR率的上限被設定至一相對小的數值(步驟S24)、該噴油時機被設定至該壓縮行程內的曲柄角度(步驟S26)、及該正常凸輪被選取作為該驅動凸輪(步驟S28)。 [0054] 當步驟S22的判斷結果是肯定時，該目標EGR率的上限被設定至一相對小的數值(步驟S30)、該噴油時機被設定至該進氣行程內的曲柄角度(步驟S32)、及該小凸輪被選取作為該驅動凸輪(步驟S34)。因此，該引擎控制是在圖3至圖4所描述的高扭矩及高速區域內被實施。當操作狀態從中等扭矩及中等速度區域轉換至該高扭矩及高速區域時，該目標EGR率或其它處理的改變係依據圖9中所描述的程序來實施。亦即，在切換至小凸輪之前，該目標EGR率和該噴油時機被改變。然後，當該進氣閥的閥關閉時間的改變被完成時，切換至小凸輪才被開始。 [0055] 步驟S12的處理及後續的處理將被描述。步驟S12的處理和上面描述的步驟S14的處理相同。接在步驟S12之後的步驟S36至S54的處理基本上和上面描述的步驟S16至S34的處理相同。關於步驟S12、S36至S54的處理的細節請參見相應步驟的描述。步驟S36、S44、S50的處理細節不同於步驟S16至S34的處理細節之處在於，該目標EGR率的上限被設定為零。這是根據步驟S10的判斷結果。 [0056] 如在上文中所描述的，根據圖10所示的常式，當導入該EGR氣體的條件以及使用小凸輪的條件這兩者被滿足時，根據描述於圖3至圖4中的操作區域的引擎控制可被實施。因此，抑制當該操作狀態從中等扭矩及中等速度區域轉換至該高扭矩及高速區域時的引擎輸出的下降變成是可能的。 [0057] 在描述於上面的第一實施例中，示於圖1中的該LPL-EGR系統36是[發明內容]中的“EGR系統”的一個例子。描述於圖3至圖4中的該中等扭矩及中等速度區域是[發明內容]中的“第一操作區域”的一個例子。描述於圖3至4中的該高扭矩及高速區域是[發明內容]中的“第二操作區域”的一個例子。該正常凸輪是[發明內容]中的“第一凸輪”的一個例子。該小凸輪是[發明內容]中的“第二凸輪”的一個例子。描述於圖5中的曲柄角度區段CA1
是[發明內容]中的“第一曲柄角度”的一個例子。曲柄角度區段CA2
是[發明內容]中的“第二曲柄角度”的一個例子。 [0058] 在描述於上面的第一實施例中，示於圖1中的該VVT 74是[發明內容]中的“轉動相位改變機構”的一個例子。 [0059] 接下來，本發明的第二實施例將參考圖11至13來描述。第二實施例的系統的基本構造和圖1所描述的構造例相同。因此，關於相同的系統構造的描述將被省略。 [0060] 圖11是一例示三種包括在依據本發明的第二實施例的系統中的進氣凸輪的凸輪輪廓的例子的解釋性圖式。如圖11所示，依據第二實施例的系統包括三種進氣凸輪：一正常凸輪；及兩種小凸輪。這兩種小凸輪是在閥開啟持續時間以及抬升量方面小於該正常凸輪的凸輪。然而，該等小凸輪中的一者具有和第一實施例的小凸輪相同的閥開啟持續時間以及抬升量。該等小凸輪中的另一者的閥開啟持續時間小於第一實施例的小凸輪，而具有等於或大於第一實施例的小凸輪的抬升量的抬升量。在下文中，為了便於描述，具有和第一實施例的小凸輪相同的凸輪輪廓的小凸輪被稱為“小凸輪(大的閥開啟持續時間)”。另一個小凸輪被稱為“小凸輪(小的閥開啟持續時間)”。 [0061] 該正常凸輪、該小凸輪(大的閥開啟持續時間)、及該小凸輪(小的閥開啟持續時間)被一和曲柄軸同步轉動的凸輪軸所支撐。和第一實施例的例子一樣地，該凸輪軸被設置有一VVT。 [0062] 在第二實施例中，使用描述於圖3中的目標EGR率及根據三種進氣凸輪的進氣閥的關閉時間的結合的引擎控制被實施。圖12例示引擎操作區域和驅動該進氣閥的凸輪之間的關係的例子。如圖12所示，在多數的操作區域內，該正常凸輪被選用。該小凸輪(大的閥開啟持續時間)只在該高扭矩及高速區域內選用。該引擎控制到目前為止和第一實施例的引擎控制是相同的。在第二實施例的引擎控制中，該小凸輪(小的閥開啟持續時間)是在低速區域被選用。更具體地，該小凸輪(小的閥開啟持續時間)是在高扭矩及低速區域和低扭矩及低速區域被選用。在第二實施例中，示於圖12中的關係被儲存在ECU的ROM中。該凸輪切換機構的切換操作係藉由將一實際的操作狀態應用到該關係上來加以控制。 [0063] 圖13是一例示該進氣閥的關閉時間的例子的解釋性圖式。如圖13所示，當該驅動凸輪是該正常凸輪時，進氣閥是在曲柄角度區段CA1
內被關閉。當該驅動凸輪是該小凸輪(大的閥開啟持續時間)時，進氣閥是在曲柄角度區段CA2
的早期被關閉。該引擎控制操作和第一實施例的引擎控制相同。在第二實施例的引擎控制中，當該驅動凸輪是該小凸輪(小的閥開啟持續時間)時，進氣閥是在曲柄角度區段CA3
(它比曲柄角度區段CA2
窄)的早期被關閉。示於圖13中的吸入效率可例如在引擎轉速和渦輪增壓壓力被固定的操作條件下被獲得。在該低引擎轉速的例子中，將吸入效率最大化的該曲柄角度被置於比高引擎轉速的例子更提前的位置。因此，雖然該區段本身的長度沒有改變，但曲柄角度區段CA3
在低引擎轉速的例子中被設置在比高引擎轉速的例子更提前的位置。 [0064] 如在第一實施例中所描述的，爆震傾向於發生在中等扭矩至高扭矩區域中。為了要應付此情況，在第二實施例中，該目標EGR率的設定係如圖3所述地被實施。此外，具有和描述於第一實施例的小凸輪相同的凸輪輪廓的小凸輪(大的閥開啟持續時間)在該高扭矩及高速區域內被選用。因此，在該高扭矩及高速區域中的爆震極限的降低可被抑制。然而，爆震傾向於發生在高扭矩區域內的事實意謂著高扭矩及低速區域亦被包括在用來抑制爆震極限降低的目標區域內。因此，當該引擎操作狀態如圖12中所示的操作線所標示地轉換時，該目標EGR率從最大值下降至目前的操作點。因此，如果該正常凸輪在該操作線的期間持續被選用的話，則雖然該爆震極限會隨著目標EGR率下降而降低，但實際壓縮比很高的狀態會持續下去。因此，為了要避免爆震的發生，除了延遲點火時機之外沒有其它選擇，而這導致了無法避免之引擎輸出下降的情況。 [0065] 為了應付此情況，在第二實施例中，該小凸輪(小的閥開啟持續時間)在該高扭矩及低速區域中被選用，使得實際壓縮比很高的狀態可被消除。如之前已描述地，該小凸輪(小的閥開啟持續時間)在閥開啟持續時間方面比該小凸輪(大的閥開啟持續時間)小。因此，當該小凸輪(小的閥開啟持續時間)被用作為驅動凸輪時，該進氣閥可以比該小凸輪(大的閥開啟持續時間)被用作為驅動凸輪的例子早被關閉，使得該實際壓縮比和吸入效率可被顯著地降低。因此，爆震極限的降低可被抑制。在該高扭矩及低速區域中，背壓低於該預定值。因此，WGV在切換至該小凸輪(小的閥開啟持續時間)之前及之後幾乎沒有被打開。亦即，在該高扭矩及低速區域中，該吸入效率被刻意地降低且點火時間的延遲係藉由切換至該小凸輪(小的閥開啟持續時間)來加以避免，使得引擎輸出被提高。 [0066] 在該第二實施例中，該小凸輪(小的閥開啟持續時間)亦在低扭矩及低速區域中被選用。因此，可以減小該低扭矩及低速區域中的抽泵損失以及藉以提高在該操作區域內的引擎輸出。 [0067] 該小凸輪(大的閥開啟持續時間)在該高扭矩及高速區域內被選用的引擎控制的特定例子可藉由將上文中關於圖8至10的描述的“小凸輪”用“小凸輪(大的閥開啟持續時間)”取代來加以描述。該小凸輪(小的閥開啟持續時間)在該高扭矩及低速區域內被選用的引擎控制的特定例子可藉由將上文中關於圖8至10的描述的“小凸輪”用“小凸輪(小的閥開啟持續時間)”取代以及進一步用“高扭矩及低速區域”取代“高扭矩及高速區域”來加以描述。該小凸輪(小的閥開啟持續時間)在該低扭矩及低速區域內被選用的引擎控制的特定例子可藉由將上文中關於圖8至10的描述的“小凸輪”用“小凸輪(小的閥開啟持續時間)”取代以及進一步用“低扭矩及低速區域”取代“高扭矩及高速區域”來加以描述。 [0068] 在上面所描述的第二實施例中，描述於圖12中的該高扭矩及低速區域是[發明內容]中的“第三操作區域”的一個例子。該小凸輪(大的閥開啟持續時間)是[發明內容]中的“第二凸輪”的一個例子。該小凸輪(小的閥開啟持續時間)是[發明內容]中的“第三凸輪”的一個例子。描述於圖13中的曲柄角度區段CA3
是[發明內容]中的“第三曲柄角度”的一個例子。 [0069] 接下來，本發明的第三實施例將參考圖14至15來描述。第三實施例的系統的基本構造和圖1所描述的構造例相同。因此，關於相同的系統構造的描述將被省略。 [0070] 第三實施例的系統是一種油電混合系統(hybrid system)，其包括內燃機以及馬達發電機(MG)作為車輛的驅動源。該混合系統包括眾所週知的構造，其除了該MG之外還包括驅動軸、動力分配裝置、動力控制單元(PCU)、及電池。因為該混合系統是眾所週知的構造，且該構造在本發明中沒有限制性，所以關於該混合系統的進一步描述將被省略。 [0071] 圖14至15為例示在依據本發明的第三實施例的系統中的冷卻系統的解釋性圖式。該第三實施例的系統包括兩個冷卻系統。圖14中所示的冷卻系統將一相對高溫的冷卻劑循環於該內燃機10、該EGR冷卻器40、及散熱器78之間。在該冷卻系統中，從散熱器78流入水泵80中的冷卻劑被送出至該內燃機10及該EGR冷卻器40，且被送回至該散熱器78。示於圖15中的冷卻系統將一相對低溫的冷卻劑循環於HV系統裝置82(例如，升壓轉換器、及PCU的逆變器)、中間冷卻器24、及散熱器84之間。在該冷卻系統中，從散熱器84流入水泵86中的冷卻劑被送出至該HV系統裝置82及該中間冷卻器24，且被送回至該散熱器84。 [0072] 如在第一實施例中描述的，當驅動凸輪在該高扭矩及高速區域內被切換至該小凸輪時，背壓隨著吸入效率的降低而下降。因為WGV的打開程度隨著背壓的下降而減小，所以可提高渦輪增壓壓力。然而，當渦輪增壓壓力提高時，該中間冷卻器內的冷卻需求亦相應地增加。因此，在冷卻劑為該中間冷卻器24和該HV系統裝置82所共用的冷卻系統(如圖15所示的冷卻系統)的例子中，該HV系統裝置82會冷卻不足。因此，在第三實施例中，被送入到圖15所示的冷卻系統的冷卻劑的溫度等於或低於一指定的溫度的條件被增加至上文所描述的第一實施例的小凸輪的使用條件中。當用於小凸輪的該等使用條件被設定時，即可避免該HV系統裝置的冷卻不足。 [0073] 第三實施例中的引擎控制的一特定的例子可藉由將關於送入到圖15所示的冷卻系統的冷卻劑的溫度的判斷加入到圖10中步驟S22關於渦輪增壓工作限制的判斷處理中來加以描述。 [0074] 其它實施例 在第一至第三實施例中，用廢氣能量來轉動渦輪的渦輪增壓器已被當作一個例子加以描述。然而，該渦輪增壓器可用一用馬達來驅動壓縮機的電子式增壓器取代、或用一用內燃機來驅動壓縮機的機械式增壓器取代。 [0075] 在第三實施例中，中間冷卻器和該HV系統裝置共用冷卻劑的冷卻系統已被當作一個例子加以描述。然而，和中間冷卻器共用冷卻劑的熱交換器並不侷限於HV系統裝置。當其它熱交換器被包括在圖15所示的冷卻系統中時，第三實施例的構造可被採用，且關於送入到圖15所示的冷卻系統的冷卻劑的溫度的判斷可被加到該小凸輪的使用條件內。[0027] Embodiments of the present invention will be described below based on the drawings. It should be noted that the same elements are marked with the same reference symbols in each drawing to omit redundant description. The following examples are not intended to limit the invention. First, the first embodiment of the present invention will be described with reference to FIGS. 1 to 10. 1 is a schematic diagram illustrating an example of the configuration of a system according to the first embodiment of the present invention. The system shown in FIG. 1 is a system for an internal combustion engine mounted on a vehicle. The system shown in FIG. 1 includes an internal combustion engine 10 as a driving source. The internal combustion engine 10 is a four-stroke cylinder engine, and is also a three-cylinder in-line engine. The number of cylinders and cylinder configuration of the internal combustion engine 10 are not particularly limited. The internal combustion engine 10 has a relatively high geometric compression ratio of 11 or higher. Each cylinder of the internal combustion engine 10 is connected to an intake pipe 12 and an exhaust pipe 14. [0030] First, a description of the intake system of the internal combustion engine 10 is provided. An air cleaner 16 is attached near the inlet of the intake pipe 12. A compressor 18a of a turbocharger 18 is provided downstream of the air cleaner 16. The compressor 18a driven by the rotation of a turbine 18b provided in the exhaust pipe 14 compresses intake air. An electronically controlled throttle valve 20 is provided downstream of the compressor 18a. An intake manifold 22 connected to the intake port of each cylinder is provided downstream of the throttle valve 20. The intake manifold 22 includes a liquid-cooled intercooler 24. The intake air flowing into the intercooler 24 is cooled by heat exchange with the coolant passing through the cooling pipe 26. [0031] A description of the exhaust system of the internal combustion engine 10 will now be provided. The exhaust pipe 14 is equipped with the turbine 18 b of the turbocharger 18. The turbine 18b is coupled with the compressor 18a. The turbine 18b is rotated by the energy of the exhaust gas flowing through the exhaust pipe 14. A bypass pipe 28 bypassing the turbine 18b is provided in the middle of the exhaust pipe 14. The bypass pipe 28 is provided with a waste gate valve (WGV) 30. The WGV 30 is opened when the exhaust pipe pressure (back pressure) on the upstream side of the turbine 18b is higher than a prescribed value. When the WGV 30 is opened, some exhaust gas flowing through the upstream portion of the turbine 18b will flow through the bypass pipe 28 into the downstream portion of the turbine 18b. The catalysts 32, 34 for cleaning the exhaust gas are provided downstream of the turbine 18b. [0032] Next, an EGR system of the internal combustion engine 10 will be described. The internal combustion engine 10 includes a low-pressure loop-EGR (LPL-EGR) system 36. The LPL-EGR system 36 includes an EGR pipe 38 that connects the portion of the exhaust pipe 14 between the catalyst 32 and the catalyst 34 to the portion of the intake pipe 12 located on the upstream side of the compressor 18a . A liquid-cooled EGR cooler 40 is provided in the middle of the EGR pipe 38. The exhaust gas (ie, external EGR gas) flowing into the EGR cooler 40 is cooled by heat exchange with the coolant passing through the condenser pipe 42. An electronically controlled EGR valve 44 is provided downstream of the EGR cooler 40. When the opening degree of the EGR valve 44 is changed, the flow rate of the external EGR gas flowing from the EGR pipe 38 into the intake pipe 12 is changed. As the degree of opening of the EGR valve 44 becomes larger, the EGR rate becomes higher. [0033] A description of the valve system of the internal combustion engine 10 will now be provided. 2 is a cam profile illustrating two types of intake cam profiles included in the system according to the first embodiment of the present invention (representing at least one of the lift amount and the valve opening duration of the cam profile, and this applies to the following Explanatory diagram of the example of ). It should be noted that "valve opening duration" refers to the length of time the valve is kept open, in degrees. As shown in FIG. 2, the system according to the first embodiment includes two kinds of intake cams: a normal cam; and a small cam. The small cam is smaller than the normal cam in terms of valve opening duration and lift amount. The normal cam and the small cam are supported by a camshaft, which rotates synchronously with a crankshaft. A pair of two normal cams and small cams are supported in each cylinder. This is because each cylinder is provided with two intake valves. However, in the present invention, the number of intake valves per cylinder may be one, or may be three or more. [0034] The camshaft supporting the normal cam and the small cam is provided with a variable valve timing mechanism (VVT). The VVT is a mechanism that changes the valve opening characteristics of the intake valve by changing the rotation phase difference of the cam valve relative to the crankshaft. The VVT includes a housing that is coupled to the crankshaft through a timing chain and the like, and a blade body that is disposed within the housing and attached to the end of the camshaft. When hydraulic pressure is supplied to the inside of a hydraulic chamber partitioned by the casing and the blade body, the blade body can be rotated relative to the casing. Therefore, the rotation phase difference of the cam shaft relative to the crank shaft can be changed. The hydraulic pressure supplied to the VVT is controlled by a hydraulic control valve provided in a hydraulic supply line. The structure of this VVT is well known. Since there is no particular limitation on the configuration of the VVT in the present invention, further description about the VVT will be omitted. [0035] Referring again to FIG. 1, a configuration example of the system will be further described. The system shown in FIG. 1 includes an electronic control unit (ECU) 50 as a controller. The ECU 50 includes random access memory (RAM), read only memory (ROM), and a microprocessor (CPU). The ECU 50 obtains signals from various sensors mounted on the vehicle and processes these signals. Such sensors include an air flow meter 52, a crank angle sensor 54, a turbocharged pressure sensor 56, a coolant temperature sensor 58, a back pressure sensor 60, and a gas temperature sensor 62. The air flow meter 52 is provided near the air cleaner 16 to detect the amount of intake air. The crank angle sensor 54 outputs a signal corresponding to the rotation angle of the crank shaft. The turbocharge pressure sensor 56 detects the pressure (turbocharge pressure) of the portion of the intake pipe on the upstream side of the throttle valve 20. The coolant temperature sensor 58 detects the temperature of the coolant in the internal combustion engine 10. The back pressure sensor 60 detects the pressure (back pressure) of the portion of the exhaust pipe on the upstream side of the turbine 18b. The gas temperature sensor 62 detects the temperature of the exhaust gas at the outlet portion of the EGR cooler 40. [0036] The ECU 50 processes the signals obtained from the various sensors, and operates various actuators according to a specified control program. Such various actuators include the throttle valve 20 and the WGV 30. The actuators also include an injector 70 that injects fuel into the cylinder, an ignition device 72 that ignites the air-fuel mixture in the cylinder, a VVT 74, and a cam switching mechanism 76 that switches the intake air that drives the intake valve Cam (hereinafter referred to as "driving cam"). [0037] FIG. 3 illustrates an example of the relationship between the target EGR rate (target value of the EGR rate) and the engine operating region. The relationship of Figure 3 was prepared based on previous simulations. As shown by the outline in FIG. 3, the target EGR rate is set to the highest value in the intermediate torque and intermediate speed region. This is to increase the EGR rate in the intermediate torque and intermediate speed region, which is particularly high in terms of frequency of use, to increase thermal efficiency. The lower target EGR rate is set to the peripheral regions farther from the intermediate torque and intermediate speed regions, and these peripheral regions are lower in terms of frequency of use. In detail, in the high torque and low torque regions, the target EGR rate is set to a value lower than the target EGR rate in the intermediate torque region. Similarly, in the high-speed region or the low-speed region, the target EGR rate is set to a value lower than the target EGR rate in the middle-speed region. In the first embodiment, the relationship shown in FIG. 3 is stored in the ROM of the ECU. The degree of opening of the EGR valve is controlled by applying the actual operating state to the relationship. [0038] In the first embodiment, in order to increase the engine output, engine control combining the target EGR rate and the intake valve closing time is implemented. FIG. 4 illustrates an example of the relationship between the engine operating area and the cam that drives the intake valve. As shown in Figure 4, in most operating areas, normal cams are selected. This small cam is only selected in the high torque and high speed area. In the first embodiment, the relationship shown in FIG. 4 is stored in the ROM of the ECU. The switching operation performed by the cam switching mechanism is controlled by applying an actual operating state to the relationship. [0039] FIG. 5 is an explanatory diagram illustrating an example of the closing time of the intake valve. As shown in FIG. 5, when the driving cam is the normal cam, the intake valve has a crank angle section CA after the bottom dead center (ABDC=0) 1 The inside is closed. When the driving cam is the small cam, the intake valve is in a crank angle section CA including the bottom dead center 2 The inside is closed. The crank angle section CA shown in FIG. 5 1 , CA 2 Has width because the closing time of the intake valve is changed by VVT. However, when a normal cam with a large amount of lift is used as the driving cam to increase the engine output in the frequently used operating area, the crank angle section CA 1 It is set to include a crank angle that provides maximum suction efficiency. When the small cam with a small lifting amount is used as the driving cam, the crank angle section CA 2 It is set to exclude the crank angle that provides maximum suction efficiency. The suction efficiency shown in FIG. 5 can be obtained under operating conditions where, for example, the engine speed and turbocharge pressure are fixed. [0040] In FIG. 5, the small cam is selected in the high-torque and high-speed region because knocking tends to occur when the normal cam is selected in this operating region. Knocking tends to occur in the range from the medium torque region to the high torque region. As described in FIG. 3, in the medium torque and medium speed region, the target EGR rate is set to a high value. This indicates that the knock limit has been increased. As described in FIG. 3, in the high-torque and high-speed region, the target EGR rate is set to a value lower than the target EGR rate in the medium-torque and medium-speed region. Therefore, when the engine operating state is switched as shown by the operating line in FIG. 3, the target EGR rate gradually increases to a maximum value, and then decreases to the current operating point. Therefore, if the normal cam is continuously selected during this period of the operation line, although the knock limit decreases as the target EGR rate decreases, the state where the actual compression ratio is high continues. Therefore, there is no other choice but to delay the ignition timing, and this leads to an unavoidable situation where the engine output drops. [0041] In order to cope with this situation, in the first embodiment, the small cam is selected in the high torque and high speed region. Therefore, the state where the actual compression ratio is high can be eliminated, and the suction efficiency can be reduced. This can suppress the drop of the knock limit and thereby avoid the delay of the ignition timing. In this high torque and high speed region, the back pressure is high. Therefore, when the normal cam is selected, the back pressure greatly exceeds the predetermined value, so the WGV is opened. However, when the normal cam is switched to the small cam, the suction efficiency is deliberately reduced, which results in a decrease in back pressure. Therefore, the degree of opening of the WGV is reduced as the back pressure becomes smaller than the predetermined value. Therefore, the turbocharge pressure can be increased to compensate for the decrease in suction efficiency caused by the selection of the small cam. This can increase the engine output. [0042] FIG. 6 is an explanatory diagram illustrating effects obtained by engine control in the first embodiment of the present invention. As shown in FIG. 6, when the normal cam is continuously selected when the EGR rate is reduced, the maximum engine output also decreases after the EGR rate decreases (dashed arrow). In the first embodiment, since the normal cam is switched to the small cam when the EGR rate is reduced, the decrease in the maximum engine output can be suppressed (solid arrow). The value of the reduced EGR rate may be zero, or may be greater than zero. [0043] Now, when the drive cam is switched from the small cam to the normal cam and the closing time of the intake valve is changed, not only does the suction efficiency decrease, but the combustion speed also decreases. FIG. 7 illustrates an example of the relationship between the closing time of the intake valve and the turbulence in the cylinder. As shown in FIG. 7, when the driving cam is a small cam, the turbulence in the cylinder becomes smaller than when the driving cam is the normal cam. Therefore, when the drive cam is switched from the normal cam to the small cam, the combustion speed can be slowed down and the engine output can be reduced. However, in the internal combustion engine having a high geometric compression ratio as shown in the first embodiment, the effect of the increase in the turbocharge pressure associated with the decrease in suction efficiency is greater than the effect of the decrease in combustion speed. Therefore, the decrease in engine output is suppressed (see FIG. 6). In this regard, in a general turbocharged engine having a geometric compression ratio of about 10, the influence of the reduction in combustion speed becomes relatively large. Therefore, the engine output tends to be reduced. [0044] Next, referring to FIG. 8, a specific example of engine control in the first embodiment will be described. FIG. 8 is a time chart illustrating an example of engine control in the first embodiment of the present invention. The time chart of FIG. 8 depicts when the operating state of the engine shifts from the area with high EGR rate (ie, medium torque and medium speed area) to the area with low target EGR rate (ie, high torque) along the operation line shown in FIG. 3. And high-speed areas) when changing various physical values and control parameters. Therefore, while the turbocharge pressure and the amount of air in the cylinder shown in FIG. 3 continue to increase substantially, the ERG rate shown in FIG. 8 at time t 1 decline. [0045] As shown in FIG. 8, the EGR rate 1 Time t 2 During the period. This is because the degree of opening of the EGR valve is changed to the closed side as the target EGR rate shown in FIG. 3 decreases. When the EGR rate decreases, the knock limit also decreases. Therefore, while the EGR rate is changed, the ignition timing is continuously changed to the retard side. As the ignition timing is retarded, a crank angle θ_Pmax (the pressure in the cylinder becomes maximum at this crank angle) moves to the retard side. [0046] In the first embodiment, the drive cam is not switched when the EGR rate is changed. The reason for this is that when the drive cam is switched from the normal cam to the small cam at the same time as the actual EGR value changes, the combustion becomes unstable and the torque fluctuation increases. In addition, the switching of the drive cam is at time t 2 (The change of the EGR rate is completed at this point in time). Switching of drive cam to time t 3 So far, they are on standby. At time t 2 It is not the change of the driving cam, but the timing of fuel injection is changed to an advanced side. The injection timing is changed from a crank angle in the compression stroke to a crank angle in the intake stroke. The reason is that when the driving cam is the normal cam, the turbulence in the cylinder can be secured and the engine output can be increased, and after the driving cam is switched to the small cam, the turbulence in the cylinder is reduced. Therefore, at time t 2 When the injection timing is advanced and changed to the crank angle in the intake stroke, the mixing of intake air and fuel can be improved, so that the reduction in engine output can be suppressed. [0047] In the first embodiment, the valve closing time of the intake valve is at time t 2 It is changed to the delay side. By controlling the hydraulic control valve of the VVT, while the driving cam is the normal cam, the valve closing time is changed to the delay side, so that the suction efficiency is consistent before and after the switching of the driving cam. 9 is an explanatory diagram illustrating an example of the relationship between the valve closing time of the intake valve and the suction efficiency. As shown in FIG. 9, the suction efficiency exhibits a characteristic substantially symmetrical to the center of the crank angle near the bottom dead center. Because of the influence of the turbocharge pressure, the crank angle at the center of symmetry does not coincide with the bottom dead center. The difference in the valve opening duration between the normal cam and the small cam is known when the phase of the cam is designed. Therefore, according to the characteristics shown in FIG. 9, the valve closing time of the intake valve (at this closing time, the suction efficiency is consistent before and after the switching of the drive cam) can be identified. [0048] The switching of the drive cam is the time t when the valve closing time of the intake valve is completed by the VVT change 3 Start. The reason for this is that when the driving cam is switched from the normal cam to the small cam and the timing of ignition changes or the valve closing time of the intake valve changes simultaneously, combustion becomes unstable and torque fluctuation increases. At time t 3 , The ignition timing is also changed to the advance side. The ignition timing is at time t 3 The advance angle of is set to a value that causes the crank angle θ_Pmax that maximizes the pressure in the cylinder and at time t 1 The crank angle θ_Pmax at the time is substantially equal. However, at time t 3 The ignition timing of is changed to time t 1 The ignition timing is even more advanced. By changing the ignition timing to this advance side, the decrease in suction efficiency and the decrease in combustion speed related to the switching of the drive cam can be compensated, and the decrease in engine output can be suppressed. [0049] As mentioned above, when the small cam is selected in the high-torque and high-speed region, the reduction of the knock limit can be suppressed. Therefore, at time t 3 Changed ignition timing at time t 3 After a period of time, it was further changed to the advance side. At time t 4 After that, when switching to the small cam is completed, the opening degree of the WGV decreases as the suction efficiency is deliberately reduced. Therefore, at time t 3 The turbocharge pressure, which tended to increase before, is at time t 4 After further improvement. The amount of air in the cylinder also follows the turbocharge pressure at time t 4 Then increase and increase. Therefore, as shown in the uppermost column in FIG. 8, it is possible to continuously increase the engine output before and after switching from the normal cam to the small cam. [0050] FIG. 10 illustrates an example of a processing routine executed by the ECU in the first embodiment of the present invention. The routine is executed during each preset control period (for example, whenever the crank shaft rotates 120 degrees). [0051] In the routine shown in FIG. 10, it is first determined whether the EGR gas can be introduced (step S10). Whether the EGR gas can be introduced is determined based on, for example, the cooling limit and the condensate limit of the EGR cooler. Examples of cooling limitations of the EGR cooler include the gas temperature at the outlet portion of the EGR cooler, the coolant temperature at the outlet portion of the EGR cooler, or the gas temperature at the upstream portion of the compressor is equal to or lower than a specified temperature. Examples of condensate restriction include that the gas temperature at the outlet of the intercooler is equal to or higher than the dew point temperature. When the EGR cooling limit is not satisfied, it is determined that the introduction of the EGR gas to improve the thermal efficiency cannot be expected. When the condensed water limit is not satisfied, it is determined that condensed water is not generated in the outlet portion of the intercooler. Therefore, when the cooling limit or the condensed water limit is not satisfied, it is determined that there is a limit for external EGR gas, and the processing of step S12 and subsequent processing are implemented (to be described in detail later). [0052] When the judgment result of step S10 is affirmative, it is judged that there is a limit to the external EGR gas, and the processing of step S14 and subsequent processing are implemented. In step S14, it is judged whether the operating state of the engine is in a high torque and high speed region. This high torque and high speed region corresponds to the operation region shown in FIG. 4. When the judgment result of step S14 is negative, the upper limit of the target EGR rate is set to a maximum value (step S16), the injection timing is set to a crank angle within the compression stroke (step S18), and the normal cam It is selected as the drive cam (step S20). Therefore, the engine control is implemented in the operation area other than the high torque and high speed area described in FIGS. 3 to 4. [0053] When the judgment result in step S14 is affirmative, it is judged whether the small cam can be used (step S22). Whether the small cam can be used is determined, for example, according to turbo working limits. Examples of turbocharging operating limits include an atmospheric pressure equal to or higher than a specified value, or the back pressure equal to or lower than a specified pressure. When the turbo charging operation limit is not satisfied, it is determined that even if the normal cam is switched to the small cam, the increase in the engine output cannot be expected. Therefore, when the turbo charging operation limit is not satisfied, the process of step S24 and subsequent processes are implemented. That is, the upper limit of the target EGR rate is set to a relatively small value (step S24), the injection timing is set to the crank angle within the compression stroke (step S26), and the normal cam is selected as the drive Cam (step S28). [0054] When the judgment result of step S22 is affirmative, the upper limit of the target EGR rate is set to a relatively small value (step S30), and the injection timing is set to the crank angle within the intake stroke (step S32) ), and the small cam is selected as the driving cam (step S34). Therefore, the engine control is implemented in the high-torque and high-speed region described in FIGS. 3 to 4. When the operating state is switched from the medium torque and medium speed region to the high torque and high speed region, the target EGR rate or other processing changes are implemented according to the procedure described in FIG. 9. That is, before switching to the small cam, the target EGR rate and the injection timing are changed. Then, when the change of the valve closing time of the intake valve is completed, switching to the small cam is started. [0055] The processing of step S12 and subsequent processing will be described. The processing of step S12 is the same as the processing of step S14 described above. The processing of steps S36 to S54 following step S12 is basically the same as the processing of steps S16 to S34 described above. For details of the processing of steps S12, S36 to S54, please refer to the description of the corresponding steps. The processing details of steps S36, S44, and S50 differ from the processing details of steps S16 to S34 in that the upper limit of the target EGR rate is set to zero. This is based on the judgment result of step S10. [0056] As described above, according to the routine shown in FIG. 10, when both the condition of introducing the EGR gas and the condition of using the small cam are satisfied, according to the description in FIGS. 3 to 4 Engine control of the operating area can be implemented. Therefore, it becomes possible to suppress a decrease in engine output when the operation state is switched from the medium torque and medium speed region to the high torque and high speed region. [0057] In the first embodiment described above, the LPL-EGR system 36 shown in FIG. 1 is an example of the "EGR system" in [Summary]. The medium torque and medium speed region described in FIGS. 3 to 4 are an example of the "first operation region" in [Summary]. The high torque and high speed region described in FIGS. 3 to 4 is an example of the "second operating region" in [Summary]. This normal cam is an example of the "first cam" in [Summary]. This small cam is an example of the "second cam" in [Summary]. The crank angle section CA described in FIG. 5 1 It is an example of the "first crank angle" in [Summary of the Invention]. Crank angle section CA 2 It is an example of the "second crank angle" in [Summary of the Invention]. [0058] In the first embodiment described above, the VVT 74 shown in FIG. 1 is an example of the "rotational phase changing mechanism" in [Summary]. [0059] Next, a second embodiment of the present invention will be described with reference to FIGS. 11 to 13. The basic configuration of the system of the second embodiment is the same as the configuration example described in FIG. 1. Therefore, the description about the same system configuration will be omitted. [0060] FIG. 11 is an explanatory diagram illustrating three examples of cam profiles of an intake cam included in a system according to a second embodiment of the present invention. As shown in FIG. 11, the system according to the second embodiment includes three intake cams: a normal cam; and two small cams. These two small cams are smaller than the normal cam in terms of the duration of valve opening and the amount of lift. However, one of the small cams has the same valve opening duration and lift amount as the small cam of the first embodiment. The valve opening duration of the other of these small cams is shorter than the small cam of the first embodiment, and has a lift amount equal to or greater than that of the small cam of the first embodiment. Hereinafter, for convenience of description, a small cam having the same cam profile as the small cam of the first embodiment is referred to as "small cam (large valve opening duration)". The other small cam is called "small cam (small valve opening duration)". [0061] The normal cam, the small cam (large valve opening duration), and the small cam (small valve opening duration) are supported by a camshaft that rotates synchronously with the crankshaft. As in the example of the first embodiment, the camshaft is provided with a VVT. [0062] In the second embodiment, engine control using a combination of the target EGR rate described in FIG. 3 and the closing time of the intake valves according to the three intake cams is implemented. FIG. 12 illustrates an example of the relationship between the engine operation area and the cam that drives the intake valve. As shown in FIG. 12, in most operation areas, the normal cam is selected. The small cam (large valve opening duration) is selected only in the high torque and high speed area. The engine control so far is the same as that of the first embodiment. In the engine control of the second embodiment, the small cam (small valve opening duration) is selected in the low speed region. More specifically, the small cam (small valve opening duration) is selected in the high torque and low speed region and the low torque and low speed region. In the second embodiment, the relationship shown in FIG. 12 is stored in the ROM of the ECU. The switching operation of the cam switching mechanism is controlled by applying an actual operating state to the relationship. [0063] FIG. 13 is an explanatory diagram illustrating an example of the closing time of the intake valve. As shown in FIG. 13, when the driving cam is the normal cam, the intake valve is in the crank angle section CA 1 The inside is closed. When the driving cam is the small cam (large valve opening duration), the intake valve is in the crank angle section CA 2 Was closed early. This engine control operation is the same as that of the first embodiment. In the engine control of the second embodiment, when the drive cam is the small cam (small valve opening duration), the intake valve is in the crank angle section CA 3 (It is greater than the crank angle section CA 2 Narrow) was closed early. The suction efficiency shown in FIG. 13 can be obtained, for example, under operating conditions where the engine speed and the turbocharge pressure are fixed. In this low engine speed example, the crank angle that maximizes the suction efficiency is placed earlier than the high engine speed example. Therefore, although the length of the section itself has not changed, the crank angle section CA 3 In the case of a low engine speed, it is set at a position earlier than the example of a high engine speed. [0064] As described in the first embodiment, knocking tends to occur in the medium to high torque region. To cope with this situation, in the second embodiment, the setting of the target EGR rate is implemented as described in FIG. 3. In addition, a small cam (large valve opening duration) having the same cam profile as the small cam described in the first embodiment is selected in this high torque and high speed region. Therefore, the reduction of the knock limit in this high torque and high speed region can be suppressed. However, the fact that knocking tends to occur in the high-torque region means that the high-torque and low-speed regions are also included in the target region for suppressing the reduction of the knocking limit. Therefore, when the engine operating state is switched as indicated by the operating line shown in FIG. 12, the target EGR rate drops from the maximum value to the current operating point. Therefore, if the normal cam is continuously selected during the operation line, although the knock limit will decrease as the target EGR rate decreases, the state where the actual compression ratio is high will continue. Therefore, in order to avoid the occurrence of knocking, there is no choice but to delay the ignition timing, and this leads to an unavoidable situation where the engine output drops. [0065] In order to cope with this situation, in the second embodiment, the small cam (small valve opening duration) is selected in the high torque and low speed region, so that the state where the actual compression ratio is high can be eliminated. As previously described, the small cam (small valve opening duration) is smaller in valve opening duration than the small cam (large valve opening duration). Therefore, when the small cam (small valve opening duration) is used as the driving cam, the intake valve can be closed earlier than the example in which the small cam (large valve opening duration) is used as the driving cam, so that The actual compression ratio and suction efficiency can be significantly reduced. Therefore, the reduction of the knock limit can be suppressed. In the high torque and low speed region, the back pressure is lower than the predetermined value. Therefore, the WGV is hardly opened before and after switching to the small cam (small valve opening duration). That is, in the high torque and low speed region, the suction efficiency is deliberately reduced and the delay of the ignition time is avoided by switching to the small cam (small valve opening duration), so that the engine output is improved. [0066] In the second embodiment, the small cam (small valve opening duration) is also selected in the low torque and low speed region. Therefore, it is possible to reduce the pumping loss in the low torque and low speed region and thereby increase the engine output in the operating region. [0067] A specific example of the engine control in which the small cam (large valve opening duration) is selected in the high torque and high speed range can be used by using the "small cam" described above with reference to FIGS. 8 to 10 "Small cam (large valve opening duration)" instead. A specific example of the engine control selected for the small cam (small valve opening duration) in the high-torque and low-speed region can be used by using the "small cam (""Small valve opening duration)" instead and further description of "high torque and high speed area" with "high torque and low speed area". A specific example of engine control in which the small cam (small valve opening duration) is selected in the low torque and low speed region can be used by using the "small cam" described above with reference to FIGS. 8 to 10 Small valve opening duration)" instead and further description of "high torque and high speed area" with "low torque and low speed area". [0068] In the second embodiment described above, the high torque and low speed region described in FIG. 12 is an example of the "third operation region" in [Summary]. This small cam (large valve opening duration) is an example of the "second cam" in [Summary of the Invention]. This small cam (small valve opening duration) is an example of the "third cam" in [Summary]. The crank angle section CA described in FIG. 13 3 It is an example of the "third crank angle" in [Summary of the Invention]. [0069] Next, a third embodiment of the present invention will be described with reference to FIGS. 14 to 15. The basic configuration of the system of the third embodiment is the same as the configuration example described in FIG. 1. Therefore, the description about the same system configuration will be omitted. [0070] The system of the third embodiment is a hybrid system that includes an internal combustion engine and a motor generator (MG) as a driving source of a vehicle. The hybrid system includes a well-known configuration that includes a drive shaft, a power distribution device, a power control unit (PCU), and a battery in addition to the MG. Since the hybrid system is a well-known configuration, and the configuration is not restrictive in the present invention, further description about the hybrid system will be omitted. [0071] FIGS. 14 to 15 are explanatory diagrams illustrating a cooling system in a system according to a third embodiment of the present invention. The system of this third embodiment includes two cooling systems. The cooling system shown in FIG. 14 circulates a relatively high-temperature coolant between the internal combustion engine 10, the EGR cooler 40, and the radiator 78. In this cooling system, the coolant flowing into the water pump 80 from the radiator 78 is sent out to the internal combustion engine 10 and the EGR cooler 40, and is sent back to the radiator 78. The cooling system shown in FIG. 15 circulates a relatively low-temperature coolant between the HV system device 82 (for example, the boost converter and the inverter of the PCU), the intercooler 24, and the radiator 84. In this cooling system, the coolant flowing into the water pump 86 from the radiator 84 is sent out to the HV system device 82 and the intercooler 24, and is returned to the radiator 84. [0072] As described in the first embodiment, when the drive cam is switched to the small cam in the high torque and high speed region, the back pressure decreases as the suction efficiency decreases. Since the opening degree of the WGV decreases as the back pressure decreases, the turbo boost pressure can be increased. However, as the turbocharger pressure increases, the cooling demand in the intercooler also increases accordingly. Therefore, in the case where the coolant is a cooling system (such as the cooling system shown in FIG. 15) shared by the intercooler 24 and the HV system device 82, the HV system device 82 may be insufficiently cooled. Therefore, in the third embodiment, the condition that the temperature of the coolant fed into the cooling system shown in FIG. 15 is equal to or lower than a specified temperature is added to the small cam of the first embodiment described above Conditions of use. When the use conditions for the small cam are set, insufficient cooling of the HV system device can be avoided. [0073] A specific example of the engine control in the third embodiment can be added to step S22 in FIG. 10 regarding the turbocharging operation by adding a judgment regarding the temperature of the coolant fed to the cooling system shown in FIG. 15 It will be described in the limit judgment process. [0074] Other Embodiments In the first to third embodiments, the turbocharger that uses exhaust gas energy to rotate the turbine has been described as an example. However, the turbocharger can be replaced by an electronic supercharger that uses a motor to drive the compressor, or a mechanical supercharger that uses an internal combustion engine to drive the compressor. [0075] In the third embodiment, the cooling system in which the intercooler and the HV system device share the coolant has been described as an example. However, the heat exchanger sharing the coolant with the intercooler is not limited to HV system devices. When other heat exchangers are included in the cooling system shown in FIG. 15, the configuration of the third embodiment can be adopted, and the judgment about the temperature of the coolant fed to the cooling system shown in FIG. 15 can be added Into the use conditions of the small cam.
